1. Field of the Invention
The present invention relates to a surface coated member and a cutting tool, which have a hard coating layer adhered to a surface of a substrate.
2. Description of Related Art
Conventionally, a surface coated member having a hard coating layer adhered to a surface of a substrate has been used for various applications. For example, a surface coated member that has a single or a plurality of hard coating layers such as a TiC layer, a TiN layer, a TiCN layer, an Al2O3 layer, or a TiAlN layer formed on a surface of a hard substrate such as cemented carbide, cermet, or ceramics is used in cutting work of metal as a cutting tool.
Recently, cutting by which a cutting edge is subject to large shock, for example, heavy interrupted cutting of metal, is increasing as cutting work becomes more efficiently. For this reason, the above-mentioned cutting tool requires further improvement in fracture resistance and in wear resistance.
However, the conventional cutting tool suffers from the following problem. That is, the hard coating layer fails to endure large shock, and it is apt to cause chipping or flaking of the hard coating layer. Such chipping or flaking may trigger accidental tool damage such as fracture of a cutting edge and occurrence of abnormal wear, thereby shortening tool life.
To improve the characteristic of the hard coating layer, Japanese Unexamined Patent Publication No. 5-220604 describes that, by forming, as a first layer, a TiCN layer exhibiting a maximum peak strength on a (422)-crystal plane, the adherence of a TiCN layer can be increased thereby to increase the adhesion to a substrate and other hard layer. Japanese Unexamined Patent Publication No. 6-158325 describes that excellent wear resistance is achieved by forming, as a second layer or succeeding layer, a TiCN layer exhibiting a maximum peak strength on a (422)-crystal plane.
On the other hand, Japanese Unexamined Patent Publication No: 6-116731 describes a plurality of coating layers in which two or more layers selected from a TiC layer, a TiN layer, and a TiCN Layer are formed on a surface of a substrate, and describes that the agreement between the diffraction plane on which a maximum peak strength is achieved in the X-ray diffraction analysis of the first layer and that of the second layer can increase adhesion between layers and also suppress a crack generated in an upper layer from extending to a Lower layer, thereby improving fracture resistance.
Japanese Unexamined Patent Publications No. 5-220604 and No. 6-158325 describe that the TiCN layer exhibiting the maximum peak strength on the (422)-crystal plane has excellent adhesion to a substrate, and excellent wear resistance.
However, under more severe cutting conditions than the cutting conditions described in a preferred embodiment of these publications, particularly under severe cutting conditions to cause accidental large shock such as heavy interrupted cutting, chipping and accidental fracture still occur, thereby shortening tool life. In addition, there is a slight difference between the performance required for a rake face and the performance required for a flank, and only bringing the crystal orientation peak on the (422)-crystal plane to be the maximum cannot satisfy these performances.
A mere agreement between the maximum peak of the first layer and that of the second layer for purposes of increasing the adhesion between the first layer and the second layer and suppressing extension of a crack, as described in Japanese Unexamined Patent Publication No. 6-116731, can improve the adhesion between layers but deteriorate the wear resistance of the second layer, failing to prolong tool life.
If the layer thickness of a hard coating layer is reduced with the purpose of preventing chipping and flaking of the hard coating layer, the hard coating layer may be vanished by wear at an early date, failing to prolong tool life. Moreover, the cutting of steel, etc. requires further improvement in fracture resistance and in wear resistance.